Could a single iron infusion help heart failure patients feel better?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age ≥18 years. * Willing and able to provide written informed consent. * Clinical diagnosis of heart failure with ejection fraction ≥40%. * New York Heart Association (NYHA) class II or III symptoms at the time of randomisation. * Ambulatory for at least 7 days prior to randomisation. * Iron deficiency defined as transferrin saturation (TSAT) \<20% or serum iron ≤13umol/L * Haemoglobin ≤15.0 g/dL. * Baseline 6-minute walk distance \<450 metres. Exclusion Criteria: * Unable or unwilling to provide informed consent. * Prior documented left ventricular ejection fraction (LVEF) \<40%. * Clinical signs or symptoms of active infection, including fever \>38°C. * Intravenous iron therapy, erythropoietin therapy, or blood transfusion within the previous 3 months. * Concurrent immunosuppressive therapy. * Known iron overload syndrome or haemochromatosis, or first-degree relative with haemochromatosis. * Known hypersensitivity to ferric derisomaltose (Monofer) or other intravenous iron preparations. * Known bleeding anaemia or haemolytic anaemia. * Any condition precluding exercise testing, including decompensated heart failure, unstable angina, obstructive cardiomyopathy, severe uncorrected valvular disease, significant musculoskeletal disease, or uncontrolled bradyarrhythmias or tachyarrhythmias. * Probable alternative explanation for symptoms in the opinion of the investigator, including severe obesity, primary pulmonary hypertension, or chronic obstructive pulmonary disease (COPD). * Severe COPD defined as FEV1 \<50%, requirement for home oxygen therapy, or chronic oral steroid therapy. * Renal replacement therapy or estimated glomerular filtration rate (eGFR) \<15 mL/min/1.73m². * Uncontrolled atrial fibrillation with resting heart rate \>110 beats/minute. * Uncontrolled hypertension with blood pressure \>180/110 mmHg. * Concurrent therapy with an erythropoiesis-stimulating agent. * Known active malignancy. * Known HIV infection or active hepatitis infection. * Pregnancy. * Decompensated liver disease.